Magnetic recording heads have utility in a magnetic disc drive storage system. There is a demand in the disc drive storage industry to develop magnetic recording heads having an increased areal storage density. However, one obstacle in achieving increased areal storage density is the “superparamagnetic limit”, which is also sometimes referred to as the “superparamagnetic effect” This well known phenomenon generally refers to the point at which the thermal activity of an object, such as the individual grains that make up a recording layer of a magnetic recording medium, is so great that the magnetization is no longer stable, i.e. the object becomes thermally unstable and incapable of maintaining it's desired magnetization.
A development that overcomes at least some of the problems associated with the superparamagnetic limit is heat assisted magnetic recording, sometimes referred to as optical assisted or thermal assisted recording (all of which will be collectively referred to herein as “heat assisted magnetic recording”). Heat assisted magnetic recording generally refers to the concept of locally heating a recording medium to reduce the coercivity of the recording medium so that the applied magnetic writing field can more easily direct the magnetization of the recording medium during the temporary magnetic softening of the recording medium caused by the heat source. The heat assisted magnetic recording allows for the use of small grain media, which is desirable for recording at increased areal densities, with a larger magnetic anisotropy at room temperature and assuring a sufficient thermal stability.
More specifically, superparamagnetic instabilities become an issue as the grain volume is reduced in order to control media noise for high areal density recording. The superparamagnetic limit is most evident when the grain volume V is sufficiently small that the inequality KuV/kBT>40 can no longer be maintained. Ku is the material's magnetic crystalline anisotropy energy density, kB is Boltzmann's constant, and T is absolute temperature. When this inequality is not satisfied, thermal energy demagnetizes the individual grains and the stored data bits will not be stable. Therefore, as the grain size is decreased in order to increase the areal density, a threshold is reached for a given material Ku and temperature T such that stable data storage is no longer feasible.
The thermal stability can be improved by employing a recording medium formed of a material with a very high Ku. However, with the available materials the recording heads are not able to provide a sufficient or high enough magnetic writing field to write on such a medium. Accordingly, it has been proposed to overcome the recording head field limitations by employing thermal energy to heat a local area on the recording medium before or at about the time of applying the magnetic write field to the medium. By heating the medium, the Ku or the coercivity is reduced such that the magnetic write field is sufficient to write to the medium. Once the medium cools to ambient temperature, the medium has a sufficiently high value of coercivity and assures thermal stability of the recorded information.
Various structures or devices have been proposed for heating a recording medium for heat assisted magnetic recording, such as, for example, a waveguide, a solid immersion lens or a surface plasmon lens. When applying a heat source to the recording medium, it is desirable to confine the heat to the track where writing is taking place. Thus, it is necessary to produce a very small, intense hot spot to heat the recording medium only in the desired location. To achieve the small, intense hot spot it has been proposed to use a near-field optical probe, such as an optical antenna, to focus optical energy through a very small aperture to produce the necessary thermal energy for heating the recording medium. Accordingly, various optical antenna designs having such a small aperture for creating the small, intense heat spot on the recording medium are known. For example, FIG. 1a illustrates a bow tie antenna 10a and FIG. 1b illustrates a circular antenna 10b, each having a small aperture area 12a and 12b respectively.
Such optical antennas are typically made from a suitable conducting material such as Au or Ag to support plasmons from a light beam that will propagate through the apertures 12a or 12b to generate the hot spot. However, such materials are generally mechanically soft and are not well suited to withstand the start/stop and intermittent contact with the recording medium that is typically existent in low flying disc recording systems.
Although it is generally known to provide an overcoat material, such as a diamond-like carbon overcoat (DLC) on the air-bearing surface (ABS) of a slider or a recording head, such an overcoat alone is not effective in protecting the proposed structures for heat assisted magnetic recording. For example, the DLC does not adhere well to the optical antenna designs formed of a material such as Au or Ag. In addition, the DLC depositions are usually done in chambers specifically designed for only DLC processing, which increases manufacturing costs.
Accordingly, there is identified a need for an improved heat assisted magnetic recording head that overcomes limitations, disadvantages, and/or shortcomings of known heat assisted magnetic recording heads.